The invention relates to improvements in apparatus for advancing, guiding and locating webs of photosensitive material, particularly for manipulating webs or strips of exposed and developed photographic films in copying machines wherein the frames of such films are imaged onto photographic paper or the like.
Photographic copying machines employ a so-called negative platform which guides an exposed and developed photographic film and further serves to properly locate a film frame in the course of the copying operation. It is important to maintain a film frame at the copying station in such position that the entire frame is flat because any portion of the frame at such station which is permitted to move out of the plane of the major portion of the frame will produce a blurred (unsharp) portion of the corresponding image on photographic paper or other suitable image receiving material. In order to ensure that the frame which is about to be imaged remains flat, many copying machines are equipped with hold down or clamping devices serving to engage, clamp and locate that portion of a film which surrounds the frame at the copying station, i.e., with devices which engage, clamp and locate the film at all four sides of a square or rectangular frame at the copying station. To this end, the copying machine employs two plate-like guide members, called masks, which define a path for successive exposed and developed films and have registering windows for that film frame which is to be imaged onto photographic paper. In order to prevent the masks from damaging (e.g., scratching) the film during intermittent transport to move the next frame into register with the windows of the masks, presently known copying machines employ devices which can be operated to move the two masks away from each other upon completion of each imaging operation. This is intended to reduce the likelihood of damage to exposed and developed films, especially by those portions of the masks which engage, clamp and locate film frames along the frame lines between neighboring frames, i.e., in regions extending at right angles to the direction of stepwise or intermittent advancement of a film through the copying station. The extent of movability of the masks away from each other is normally selected in such a way that the retracted masks are out of contact with the film before the film is set in motion in order to advance the next frame to a position of register with the two windows.
In many instances, one of the masks is located below the other mask. The need for movability of the lower mask creates many problems in certain types of copying machines, especially in those which are utilized in so-called minilabs, because the space beneath the path for the film across the copying station is at a premium. The lower mask is located between the film path and the so-called positive platform which supports and guides photographic paper for movement past the copying station.